Our studies are designed to delineate the neuronal response to noxious stimulation of the periphery and nerve injury. The dorsal root ganglion and spinal cord are the first levels of processing of neuronal information. Using cellular and molecular techniques, we are able to identify important elements in this neuronal network. Excitotoxicity induced neuronal loss has been proposed as a possible cause of some types of chronic pain states. Calcium-binding proteins may function to buffer the effects of an excessive neuronal barrage. We have studied calretinin (CR) a recently identified calcium-binding protein using immunocytochemical techniques. CR immunoreactivity is present in a small subpopulation of dorsal root ganglia neurons and neurons in many spinal cord laminae. In the spinal cord the densest axonal and cell body staining occurs in laminae I and II, an important area for processing of noxious inputs. The spinal distribution of CR is unique from that of other calcium binding proteins. Experiments are underway to examine regulation of calcium-binding proteins in animal models of nerve injury and nociception. Nitric oxide (NO), a free radial gas, has been proposed to be a novel neuronal messenger molecule. One potential role for this gas is in excitotoxicity. Using in situ hybridization histochemistry, RNA blot analysis, and NADPH histochemistry we have localized NO to subpopulations of dorsal root ganglion neurons and spinal cord neurons. Following nerve injury, nitric oxide synthase is induced in dorsal root ganglion neurons. The subpopulation of neurons containing NO likely play important roles in nerve injury and nociception.